Large traction vehicles such as locomotives are typically powered by electric traction motors coupled to axles of the vehicle. For example, a locomotive commonly has at least four sets of axles, typically six, and corresponding wheels per vehicle, with each set being connected via appropriate gearing to the drive shaft of an electric motor, referred to in the art as a traction motor. Traction motors, when operable, are supplied with electric current from a controlled source of power, commonly a traction alternator driven by the locomotive's engine. The traction motors apply torque to the locomotive's wheels, which in turn exert tractive effort on the rails on which the locomotive is travelling.
Locomotives are normally expected to produce high tractive efforts. Good adhesion between each wheel and the surface of the rail contributes to the efficient operation of the locomotive. The ability to produce high tractive efforts depends on the available or achievable adhesion between the wheel and rail. Certain rail conditions such as being wet or covered in ice/snow may require the application of a friction enhancing agent such as sand to be applied to the rails to improve the adhesion of the wheel to the rail. To achieve this, locomotives are equipped with sand boxes on either end of the unit and nozzles to dispense the sand to the rail on either side of the unit.
Locomotives may improve adhesion by initiating a flow of sand from the sand boxes to the rail surface. The flow of sand may be initiated in response to certain conditions being met, such as one or more wheel axles slipping. When one or more of these conditions is/are met, typical sanding systems will activate a flow of sand through sand applicators located at the appropriate wheels based on the direction of travel. Sand is normally dispensed at a fixed rate each time there is a demand for sanding from the locomotive control system. Sanding may also be applied manually by the operator. Manual application of sand may be used whenever the operator feels that it will assist in the performance of the locomotive.
An emergency sanding switch (ESS) may be activated whenever the locomotive's pneumatic brakes are placed into a penalty or emergency status. Both situations are used when a fast train stop is requested by the operator. As a safety requirement, all trains, once properly connected, in the correct sequence, and thus ready to move (i.e. “made up”), undergo complete testing of the brake systems to ensure that all brake cylinders on the whole train are functional. Some of the tests include placing the brake system into penalty application as well as emergency, both cases resulting in the ESS being activated.
In both cases, with the locomotive being at a standstill, a significant amount of sand is wasted, which is both costly and without real benefit, since the sand is not needed when the locomotive is not moving. Moreover, the sand that is dispensed during such testing may foul up the tracks and thus when the locomotive begins to move again, the attached cars would ride over the sand, which adds unnecessary wear to the train's components and drag to the pulling locomotives.